assult and possession of a deadly weapon.

There's a variety of information that is missing from your question that's going to help determine the possible sentence your boyfriend can get.

1) What's he on probation for?

2) What kind of weapon did he have?

3) What degree of assault was he charged with for spitting on the girl?

You should seek out the advice of a local lawyer quickly with as much information as you can get.

Your factual description appears to involve misdemeanors. If that is the case, the maximum jail sentence is 364 days in the county jail. However, multiple counts could result in multiple 364-day sentences, running consecutively.

I strongly urge you to seek exceptionally qualified legal help.

This is more of a guess, but if he is already on probation, you would think he could get a year or more. I am not saying he would get that, but her certainly could.