How can I make my marriage better?

I think the first part of your question is around the idea of resolving disagreements with the idea of agree to disagree. It sounds like you're experiencing a negative impact from this style of resolution management. 

You also mentioned that your wife is saying that you don't keep your word immediately after saying that 'agree to disagree' is hurting your marriage. That implies a connection to the issue around agree to disagree. It sounds like something that may be happening is that issues are being brought up repeatedly after agreeing to disagree on a particular point, issue or resolution. That sense that things could be re-argued at any time can leave things feeling unresolved or even creating the potential for your wife to feel under emotional attack if issues she believes were resolved are suddenly brought up. 

First issue, agree to disagree can be effective resolution to disagreements under certain circumstances. If there is a sincere understanding that each person's viewpoint is valid. If there is a pathway to address the underlying issue/concern/complaint that ignited the disagreement.

Agree to disagree is not effective when there is not an equal display of respect. It is not effective if the issue/concern/complaint is re-introduced frequently during subsequent disagreements. It is not effective if it is used to make an argument end rather than resolve the conflict.

Other methods that may be more effective than agree to disagree

1. Stick to one topic of discussion at a time. (Address one issue or hurt at a time to effectively resolve a source of stress between you)
2. Keep your language respectful. (Disrespectful words, attitude and tone activates defensiveness which can make it very challenging to truly resolve a conflict)
3. Listen while your wife is talking (This may seem simple but it is very easy to fall into listening to respond rather than really listening to what you partner is feeling and how they are expressing their needs)
4. Focus on resolution of what to do moving forward. (This could look like "I understand you feel X. What can I do to help you in the future" or "I know this was frustrating/annoying/upsetting. I want to help both of us address this better. Next time this happens what would help you feel loved/seen/appreciated")
5. Check-in emotionally throughout the disagreement to see if you are calm enough to continue in having a respectful conversation. If you aren't or your wife isn't then give each other permission to take a break. (To practice new skills it is really important to regulate within yourself)

You also mentioned that your wife says you have trust issues. That could be related to so many things (accusations that come up only during arguments, needing to be reassured that she wants to be with you, general distrust of other people etc). I am not exactly sure what inspires your wife to say that. I will say that issues with trust can definitely be related to mental and emotional health. Having support in exploring trust and worldview could be really helpful in learning to discern who to trust and how to exercise trust.