I'm glad that your friend seems to be on the up-and-up about this - I had a very bad experience with my high school best friend writing me a bad check.
I had loaned him the money to pay his rent - I think he needed to cover two months - and he wrote me a check to pay it back. It appeared to post into my account...and I left on my previously scheduled vacation. I had some unexpected expenses (had to get a hotel room for a couple extra days instead of staying with a friend as I had planned) and so had dipped further into my bank account than I had originally budgeted, but there was still a fair bit of money in it. When I checked my bank account towards the end of my trip I saw that I had gone from $$$ to a negative balance! I called and found out that it was because the check from my friend had been returned and a fairly hefty fee had been assessed, along with a couple of overdraft fees when my trip spending and a few autopay bills exceeded what was left in my checking account.
My friend claimed that the check had been written off an old closed account with an identical checkbook, but couldn't explain why he didn't have the whole sum of the money he owed me - or how he didn't notice it not having come out of his account when he looked at it online! He ended up paying back a token amount and then our friendship more or less just...ended.