I’m tired of feeling this way

my wife and I been married for 5 years now we share a 2 year old son. Recenlty we decided to seperate due to arguments and bumping head a lot she was the main one that said she wanted to work on herself and learn to live herself which I understand I'm okay with it we recently seperated for 3 weeks now on our first week seperated she started hanging out and talking to this friend. Short story short my wife told me her and that friend like each other and there going to see where goes. I was shocked that this was happening so fast she told me that she never meant for it to happen that it happen and that her friend makes her really happy. My wife and her friend talk like 6 times a day. She been ignoring.our son. most of the day to go talk to her friend so I been the main one taking care of our son. She said she wanted to stay marry so I can help her go to college through my benefit I recently got out of the military so l have benefits for college to her get in. It making me feel used even more the fact that she is pretty much talking to somebody else.

Recently I been trying my best to be as understanding about this because I'm trying to be in good terms with my wite for our son but it's killing me and we been getting into an argument this past 2 days.

Like today we got into an argument because she bought some vitamins and she didn't tell me which I didn't mind her buying it because she needs them. She was on the phone with her friend and she was telling her friend how she pretty much bought it with her own money like trying to impress her friend. (we have a joint account where we share the money) She got mad because I told her she didn't tell me about buying vitamins and she misunderstood me as something else like I was being controlling. I was confuse because me and her always discuss about our spendings and finances. I was just surprise she got mad at me because everytime when I buy something and I always have to tell her about my spendings if not she gets really mad at me. More of a back story we both don't currently have jobs the only income we're getting is my disability

check. I'm currently still looking for a job. My wife also tried to argue that I should be the only one to work so she can stay at home with our son. But it just doesn't sit right with me knowing she talking to somebody else while I work it makes me feel used in a way and she also said to help her get an apartment and help pay for it till she can get back on her feet once our lease is up in September. We just figuring stuff out still. Just need advice because I feel like I'm losing my mind sometimes because my wife talks to her friend aka lover in front of me and everywhere around the house and it's hurts me hearing them talk on the phone l've tried addressing it to her and at first she told me she felt bad but now she really doesn't care and tells me to just accept it and to stop talking to her about it and stop making it her problem because her friend (lover) is what is making her happy. I honestly cry myself to sleep because I didn't expect for all of this to happen just need advice or anything. Just want to take full custody of my son and get a divorce. But I just need advice