Imagine that it's the beginning of September and the brother is not fine yet.
A: This summer was horrible, I didn't even get to go anywhere. We have been struggling for my brother to recover from his accident. What did you do this summer instead?
B: Well we did many things and I had a lot of fun, now for example I'm in New York and I'm loving everything about it. Over this summer I've thought many times about texting you but I've never done that because I didn't want to disturb you. I hope your brother gets better soon.
I was wondering whether can we mix present perfect and past simple this way or should I always stick to one of this two tenses when using "this Summer" and others? Because more than anything I'm not sure about mixing past simple(because from my point of view Summer is over) with present perfect (because my brother hasn't recovered yet). Plus from B's point of view summer is not over since they are still on a vacation.
Best Answer
You should use the appropriate tense at each point. You start talking about the summer in the past tense. No problem here.
Next you change to the present perfect. That's not an error. But the use of the word struggling is awkward, it looks like translationese. Better to use past tense for the accident and present perfect for your current state:
"B" can also use whatever tense is appropriate. First sentence is about the past, so past tense. Second sentence is about the present, so present tense. The "I'm loving" is casual (continuous tense of stative verb), but I think acceptable here
A sentence can have mixed tense:
Each finite clause has its own tense, and while jumping around tenses too much is confusing for the reader, and bad style, it is not incorrect.