They're very different. 1. 'Mull' usually goes with 'over'. If you mull something over, you think about it, usually to come to a conclusion or come up with an idea. 'I've been mulling over what you said yesterday, and I've come to the conclusion that you're right.' 'Hmm. I'm not ready to make a decision yet. Can I have some time to mull it over?' 2. 'Dwell on something' means to think about something negative for too long, when you ought to forget about it. 'I know you made a bad decision, but it's not good to dwell on it for too long. Just learn from your mistakes and move on.'

Hi, I would use dwell in a past tense or about something unhappy and mull in the present (when you are thinking or considering something. For example: I won't dwell over the decisions I've made There is no point dwelling on the past I'm mulling over the new job offer I'll mull over it for a while Hope that helps

I would kindly suggest that you spell your words and not use texting shortcuts (sth)