OP, you say that he makes time for the gym etc., surely he can go to the gym every morning and every night while working away, if he really wants to, so then when he's at home, he could have that extra time in the morning, sleeping in, and then stay up an hour later to spend time with you? Just a thought.
I too have been through this, the feeling of I'm John's wife, I'm Jack & Susie's mum, but who am I, is a question many, many women ask themselves. I do get the impression that your husband is actually very selfish, and the longer this goes on, the worse it will get. When my ex and I eventually split up, and he married someone else, he actually said to me that his work was "more important than ANYTHING else", I couldn't believe what he said, so asked him if it was more important than his new wife, and he just repeated "my work is more important to me than ANYTHING else". Eventually he was made redundant from the job that he had put before ANYTHING else, and he was left with having to start over, when he was a lot older. By this time we'd stopped talking as our children were grown up, but I'd love to know how he felt about his work then!
Having said all that, I think you need to talk to your husband, and if he tells you you're being ridiculous, irrational, or whatever, you should try saying, "I may be being ridiculous / irrational, but it's the way I feel, and you NEED to listen to me". I found when I said this to my new partner, that it stopped him in his tracks, we then sat down and talked about the matter in hand, and sorted things out. Of course this may not work with your DH, but it has to be worth a try.
At the end of the day, he's either seeing someone else, or he's risking you seeing someone else, and I'm afraid I'm getting the impression that he wouldn't really care if you were, and if you did, in view of his past history, it would serve him right.
Sorry this is so long, but just one more thought, are you absolutely SURE that he's working away every time he tells you he is? Maybe try ringing the hotel where he's supposed to be staying, and check that he's there, as it would be so easy for him to be somewhere else, now that we all have mobile phones.