Is my husband up to something?

First of all, just a little bit of context: I got married when I was 16, him 25, because I was pregnant. We had been seing each other for a year previous. He wanted to do the right thing so we got married. It's been 17 years now, we have a 16 year old son who will turn 17 in September.
His behaviour is very tender towards me, however, he had cheated on me in the past. Seven years ago I found out he was having what seemed to be a serious affair and that he was thinking of leaving, yet he didn't tell me about it. When I found out I begged him not to leave me and he didn't - well, he left for two weeks, then consumed with guilt and wanting to do what's right, he came home. I don't know if he cheated on me prior to that, even if it was for one night stands, but I think it's possible.
We then tried to save our marriage by moving to a different state (we're brazilian by the way) and starting all over. However, two years ago things hit a rough patch again. You see, I'm a nurse and I work most nights, so I spend most nights away from him and also weekends. But well, this gives me good money! He's complained about my shifts, that he's had enough of spending the nights alone. He then changes subject because he's not the type of person who talks about things that bother him, but sometimes I see he's upset about something but won't say. For him it's most important to be at peace with everyone.
Also, he's complained that he's always alone socially and that people are always asking where I am, and why he's alone. But well, I really have to work a lot to earn my money! It's true that I love to go shopping yes and have money to go to the hairdresser whenever I want, but is that so wrong? I also do this because he's a lawyer but doesn't make that much money, he settles for anything, he could have gone more far in his career and he didn't. He does go with me everywhere tough, dinner with my girl friends, etc, but maybe it's out of this feeling of obligation that seems to guide hum and not out of love. Could it be he sees me as a daughter, someone to take care of?

Anyway: two years ago he found on facebook that he had family across the ocean, in another continent - he's always been very interested in his roots and couldn't wait to meet them. I didn't want him to go, I've never been "alone" in my country, I cried and said I'd rather spend the money (that he didn't really have) in a new kitchen. So he postponed the trip and he cried every single day. I hadn't seen him cry for years. He even said he wanted the Lord to take him.

Anyway, he did go on his trip - without me. I said it wasn't the best time for me, nor am I willing to spend my money in a trip with his family, there's really not much there for me. He went by himself. Is this alright? He came back a different man. More introspective, more distant, and talking about them all the time, specially about a distant cousin (WOMAN) who's almost 30. He then quit talking about her.
He's then mentioned divorce once or twice, but then drops the issue (I drop it too cause I don't wanna hear about it) and is caring again. Could it be that he's just used to me, to our routine, to our friendship and secure life?

Then, three months later, goes away again without me for 10 days, says work trip. And three months later, another work trip, this time is cell is always off. Meanwhile a distant man at home. And five months later, tells me he'll leave and don't know when he'll come back. Sais he needed to find himself, be alone. What?? Well, he left and no cell phone, just an email here and there telling me he loved me. He was one month away before returning because I was having an operation, nothing much but he felt he had to be with me then, and came back. Three months later, another month away from home - to supposedly work on a family's vacation home. Hardly called. I went after him, there he was and he confessed - "I'm going away for 10 days to see my family (other country, continent). No matter what you say you can't stop me".

WTF is this, could he be having an affair or something? However most man don't do this, always this will to be away from home...when he is with me, he seems to have my best interests in sight, he's a GREAT father, always worried with our son, but then can't wait to go away and be away from me!

Could it be he's with me out of obligation? Does he not care anymore? Am I crazy thinking one day he may leave me for good? Cause all this absences, and distance, in spite of our pacific relationship (I don't bother him much) don't seem to be good at all.