Can you use past and present tense in the same sentence?

In your first sentence, you switch from past to present tense where the second clause is a temporal qualifier, which is not allowed.

"...he comes over quite often, he and I got on quite well when we see each other so not much issue there."

A more extreme example of this not being right might be, 'I was tired when I am hungry'.

Your second sentence is correct, because the tense matches.

To answer your title, which is broader, you can combine tenses in a sentence if they are in separate clauses but remember to match tense when you use 'when'. An allowable example without 'when':

I have to get my hair cut because I was told that it is too long by my teacher.