My actions shouldn't be hurting my partner; can I still acknowledge the hurt and want to help?

Yes, it is possible to acknowledge someone's pain without necessarily isolating yourself from your social support system. It sounds like your partner is having a reaction to you socializing with someone else at work. It sounds like you and this friend speak to each other quite a bit and that makes your partner feel uneasy about the situation. When you say that you speak to your friend more, do you mean when you are at work or in general?

If you are referring to speaking to this friend more at work because you two are coworkers, it makes sense that you would speak more to others especially as effective communication may be a big part of your job. And getting along with your coworkers can help us feel more comfortable and happy in a work environment.

If you are speaking more to your friend than your partner (in general), what makes you feel more comfortable in speaking to your friend over your partner? I would definitely think about the content of the conversations as well. For instance, it is very understandable that speaking to coworkers about different topics (depending on our comfort level) as we spend a lot of time with them. But then does this mean, you wouldn't feel comfortable speaking to your partner about these themes as well? If there is an issue, it may be worthwhile exploring why this is the case. Has your partner made you feel safe to express these things with her? Depending on the answer to these questions, it may be helpful to help her understand the way you feel and why you share/don't share certain things with her.

It may be difficult to see your partner feeling more comfortable speaking to someone else about issues you don't feel comfortable speaking to her about... and this is where you can acknowledge the hurt and discuss why this is the case. For example, there are times when someone may feel like they can't talk about a hobby, such as sports. That person's partner may dislike sports altogether and doesn't want to hear updates about who is winning or losing. And if there is a coworker who does want to talk to you about this, it makes sense that you would gravitate to speak to them over your partner about sports. But if you are seeing a pattern of many topics you don't feel comfortable sharing with your partner, it may be worthwhile considering why this is the case. 

Now if you feel comfortable speaking to both your partner and someone else about these topics, then it seems like you are being open with both. So perhaps exploring your partner's concerns about different types of friendships that you may have with others while you are in a relationship may be helpful. For instance, are there topics that you two want to keep private, which would mean that you only discuss with each other? And if so, can you two discuss it together? Sometimes there may be a fear of sharing certain details about your partner with others or personal information that you both may not want shared with others. And if this is the case, how can you two reassure each other that you will keep certain things just between each other? Granted venting about each other to friends is a healthy way to process emotions. In addition, getting an outside perspective can be helpful at times as well. Also reassuring each other that even though you two care a lot about each other, you two may need some space at times so that you two can continue being good partners to each other. 

Also, what are the concerns that your partner has about this friend? Is it just with this friend or friends in general? Does your partner have a hard time trusting? Has there been a reason that your partner has felt that she can't trust you? All of these questions are worthwhile considering as it will help you determine if there is a reason why your partner feels the way that she does. And if not, having your partner explore or figure out where these insecurities are coming from might be helpful to explore.

Spending time with friends or others outside of the relationship is a healthy component in any relationship. It allows you both to miss each other, have different connections with others, but also an opportunity to share these experiences with your partner. For instance, if you go to a restaurant with friends to catch up, you can share with your partner what a great time you had as you haven't seen them in a while. There is more to you than just being a partner and sometimes these parts come out when we are around others. Sharing this with your partner can help her better understand who you are as a person. One way to be in tune with this is by having time to yourself or with others. Is this something that your partner is open to doing? Also, is she willing to do this as well for herself? A balance of this can definitely help you both take care of yourselves as well as be better partners to each other. 

I would definitely recommend having a conversation with your partner about effective communication and having healthy relationships with others outside of the relationship. There are also some great self-help books out there that discuss healthy relationships and effective communication other there. Some examples are:

1) Non-Violent Communication by Marshall Rosenberg

2) Set Boundaries Find Peace by Nedra Glover Tawwab

3) The Power of Attachment by Diane Poole Heller

If you feel like you need additional support, I would encourage you to consider getting your own personal therapy and/or couple's counseling. In addition, you can also encourage your partner to get her own therapy services as this may help you both better understand yourselves or each other. Best of luck to you and your partner with everything.