need some opinions please helpp (kind of long)

Ever since I got pregnant it's like me and SO never stop fighting. I miss him to death when we're not together and just want him with me but when we're together I always seem to be mad at him and starting fights..it's getting to the point where I took a number out of his phone and texted the girl asking who she was even though I 100% trust him and don't think he would cheat. I think I'm just scared about what if we don't work out after the baby. He has a son with someone else and they only lasted till the baby was 4 months old. Plus I'm going through a lot family wise my dad is getting chemo right now also. I just don't know what the fuck I'm doing anymore or what to do to get things back on the right foot