What is it that you're upset about: that he masturbates or that he uses something at least some of the time to make it feel better?
I have a Fleshlight too. It gives an extremely good physical simulation of the sensations of intercourse. However emotionally, it's still very definitely masturbation and there are none of the other aspects to partner sex, especially in a loving relationship.
If all he wanted sexually was the physical side, he wouldn't be in a relationship with you. If he was going 'I don't want to have sex with you, I want to stay in my flat and masturbate, you'd have grounds for complaint. But that's not what's happening, is it?
The 'I should be enough for them' is a horrible road to put yourself down. You wouldn't, I hope, say that you're the only person he should talk to and expecting to be someone's only sexual outlet is... optimistic. You've probably never been and never will be in a relationship with a man who doesn't masturbate sometimes. People, men and women, often masturbate in relationships. Sometimes there's a physical separation - you don't sleep together every night, I take it; sometimes one person is more interested in sex than the other; sometimes someone wants some 'just for me' time; sometimes they want added variety; etc etc etc.
I bought my Fleshlight while I was in the relationship I am still in, years later. We went on a holiday somewhere, saw one in a sexuality shop along with a demo by the (female) shop owner and I decided to get one. It is great, but it's very much an 'as well as' not an 'instead of' the sexual side of our relationship.