Is my sex drive causing my man to feel insecure?

Firstly I apologize for how long this is. I have an amazing boyfriend, 32y. o. and I'm 31. We have the best relationship I have ever had (together for 2 years this coming Monday :). I am divorced with a 3 yo son, and my boyfriend lives with us. I am the first woman he has lived with and ever talked about being with forever. I know he loves me and is so supportive all around. He was previously a ladies man and I know he has been with many women. Lately I feel like he has been more insecure than I had realized. He knows that I am horny, like a lot. I could easily have sex every day. He knows I masturbate and I know he does and he has seemed weird a few times when he found out I have vibrators. He recently found out I had gotten a new one. Anyway over the last 6 months or so he has made comments about feeling fat or ugly, few and far between but much more often then before. I honestly was so taken aback by these comments. Especially since I have always felt that he is maybe slightly more "Hot" than I am. He's a very good looking guy and in reletively good shape (Aprox. 6'1" 195lbs). I have had a child so my body is nothing to brag about due to some stretch marks and about 15 pounds to lose. Well I have been working out a lot and am going to be training for a professional bikini (bodybuilding but not bulky) contest coming in April. Which he is so supportive about and wants to help me pay for the costs since it's always been something I've wanted to do.

Anyway I have noticed that he has been masturbating more these days since having gotten his first smart phone. Almost on a daily basis while at work on his break. This is so weird to me. Previous to the new phone he shared my computer and never cleared the history since he's not computer savvy, and usually only did it once a week on his day off. But there have been a few times now where he has gone limp during sex the same day he has watched porn. I have been afraid it's the porn but now I'm wondering if it all comes down to insecurities on his part. He has also been stressed financially recently. He use to have his own business but had closed it down a few years ago. He shared it with a family member and all of a sudden there was a tax levy placed on his bank account. After he told me he asked if I thought he was a loser. I told him of course not! Shit happens, hell I'm in the process of filing bankruptcy since my divorce and he is aware of that. He's cashing his checks now so he still has money and has not seemed any more stressed since it initially happened about two weeks ago.

We have sex a few times a week and it's great unless he goes limp which has happened twice this past week and a half. I have only ever asked him one time the next day if it was alright for him. I always tell him how hot he is and how great sex with him is. I have never wanted it so much and I attributte it to our great sex since thats what I always think about when I masturbate. Is this normal for guys? Do you think this is more stress related, the increase in porn use and the problems with maintaining an erection? Or is this an insecurity thing? Has me expressing my constant want for sex made him feel insecure about it? And if so what can I do to help him?

Again thanks for reading all of this if you have! I love this man with all my heart but this is starting to make me feel bad about myself. When normally I'm very confident. :(