Loneliness can drive most of us to do things we regret later. Good on you for recognizing the problem and reaching out for help.

I think if you set up some sort of distraction/reward, maybe cue up a favourite film, so you're ready with something comforting and enjoyable to distract you from you loneliness when you say no.

I think you'll find the strength, you already know you need to do this for yourself. Just focus on how crummy you feel afterwards, and how proud of yourself you'll feel when you say no.