My husband wants to separate after a fight and doesn't even want to give this marriage a 2nd chance
Hello. I want to first say that I am sorry that you are going through such a challenging time with your husband. I don't see so much a question here, but a narrative that describes what you are going through. To respond to this, I will do my best to share some observations that maybe useful for reflection.
You and your husband were friends for 12 years before marrying a year and a half ago. You previously lived in different states. It sounds like you knew each other and perhaps had expectations based on knowing one another from a distance.
The two of you moved in with his parents and then you went to see your father due to a medical emergency. While you were away, he talked to his family about your relationship and now they don't like you and have encouraged him to leave you. I read your description of his family and their involvement and it sounds like you believe this is their doing. I can see why you think that but in the end it doesn't change what his position is. If he wanted to stay with you he would stay with you. It is possible that he felt this way for longer than you realize and did not feel that he could tell you for any number of reasons such as being afraid to fight or hurt you. Being with his family has perhaps given him the support he needs to be true to himself and to let you know he is unhappy and does not want to stay in the marriage.
You have begged for a second chance and he refuses to give you one. While it's reasonable that you want to stay in your marriage, he is within his rights to also want to leave the marriage.
You said that you "have done everything for him and his family" and so you now feel a sense of betrayal. If his commitment and feelings are not there for you, no amount of favors for his family are likely to change that. It is reasonable that you feel some hurt and resentment toward his family and him but this is a very transactional perspective. Doing favors for someone does not oblige someone to stay married to another person.
You are well with your rights to feel frustrated and confused. Based on what you shared, it sounds like you did not expect him to leave you and that you did not see this coming. You said that you are "not even trying to feel better" because that will mean you are trying to forget him and then there will be no hope. As a reader of your troubles, this to me, is maybe the most important part of this narrative. Trying to feel better is about just taking care of yourself and has nothing to do with trying to forget him or losing hope. Your perspective suggests that you believe he has some type of duty to stay with you. Relationships and love flourish when everyone is choosing to be in them. Even if he gave things another chance, after all of this, what would you do with the hurt and resentment that has crescendoed to involve family in this way? Back to the idea of "feeling better," you are likely to feel a lot of hurt feelings throughout this separation. This is normal. Feeling better is a normal part of working through grief. I read this as you potentially hanging on to resentment and this will not serve you. Working toward accepting his decision is the only thing you can do at this point. You can't make someone be in a relationship with you. Provide yourself comfort, seek support from your own family and unless you hear something different from this guy, start doing what you need to do to let him go.