Eat more home-made tomato soup! And lots of cherries - that are in season now.
And all the other wonderful unprocessed plant based foods that are good for enhancing your mood.
Do some form of exercise for a few minutes a few times a week where you pulse is racing and you're out of breath.
That's the physical stuff that - according to the science - has a good chance of elevating your mood.
Then it's a case of working on the mental stuff to overcome your anxiety. Taking yourself less seriously, being less perfectionist, using negative stuff that happens as the ingredients for amusing anecdotes, being more pragmatic, focusing on the positives more. Face down your fears. Take a zoomed out look at your life.
Read Dale Carnegie's How to Stop Worrying and Start Living.
If I were to say to you "Don't look at the Ferrari that's parked outside the window." what would your reaction be and what would you be thinking?
Every time you ask or tell your boyfriend to not look at other girls, what's he going to be thinking and feeling?
Every time you tell him not to get attracted to other women, what's he going to think and feel?
Don't think of the pink elephant.
Don't think of the pink elephant!
DON'T think of the pink elephant!
Don't THINK of the pink elephant!
Don't think of the pink ELEPHANT!
Whatever you do, don't mention the war!
Your boyfriend has been spinning you a lot of lies. His lies are entirely understandable due to your unreasonableness on this issue. Every man in the world will find other women attractive. Just as every woman in the world will find other men attractive.
It's fine. It's still possible to have a faithful, loving, genuine, one on one, exclusive, till death do you part relationship in these circumstances. Billions of people worldwide are in such a relationship.