My boyfriend and I have been dating less than a year, at first I was maybe half a stone overweight and we had sex regularly, then I started gaining weight and sex went down hill, I questioned him and he said he was stressed, then I became pregnant and have ballooned out to 14 stone, sex is once every 3 weeks, I questioned him again and he said he finds me unattractive, this has seriously messed my head up, and he constantly looks at porn,I've tried to leave but he claims he loves me and things will get better, I'm confused as I am pregnant and feel I failure if we split now :-(

Love and physical attraction don't have to go together. Watching porn doesn't mean he doesn't love you. It's better that he is honest about his feelings. Would you feel differently about sex if he gained a comparable amount of weight?
I hope you are under doctor's care while pregnant. You want to avoid gestational diabetes and other possible conditions. 14 stone (196 pounds) is a lot unless you are very tall.
Pregnancy hormones can do a number on your emotions. Try to get through the birth and assess the problem afterwards.
Countless men watch porn in addition to a loving relationship, with sex. It's when it takes over and excludes affection and touching that it's a problem. Let him know that you need some tenderness and touching while pregnant even if it doesn't lead to sex. If he can't even do that, answer back.

Thanks but I probably should have mentioned that sex is a very important part of the relationship for me, he has also gained weight and has a skin condition but I choose to look past this, he'd rather masturbate watching porn than make love to me, knowing how I feel :-(

What's his skin condition? Does it get worse with exercise, sweat, contact/rubbing, as many do? Is he being treated for it? Are you getting OB/GYN care?

We all make choices based on what we have in front of us.
You didn't take the pill or get an IUD, and got pregnant.
You gained weight.
You have a child to think about, fathered by a man who loves you but doesn't desire you.
BUT
You want to be desirable and to have more sex.

Clearly these don't mesh. You can't Always Get What You Want, as the song goes.
Some choices are:
1. Work on a way to mutually masturbate/cuddle/stroke that is a compromise on both your parts, a way to keep you together. You may have to discuss this in a seemingly cold and practical way, with certain days and times per week set aside for it. You get some of what you want, and he gets to watch X amount of porn, as well as masturbate sometimes.
2. Get counseling together.
3. Postpone all of this until after the baby is born.
4. Leave him.

Most likely he is masturbating and taking care of his sex needs there. And to be blunt, a little weight, esp while pregnant, is to be expected.

He has to deal with this,

Thank you, u both have been very helpful,