My fiancé lived with his mom for approx. 2.5 months before he moved out. He graduated high school 6/18 and started bootcamp 7/23/18. Can his mom claim him on her taxes?

You can claim a child, relative, friend, or fiance (etc.) as a dependent on your 2018 taxes as long as they meet the following requirements:

Qualifying child

• They are related to you.
• They aren't claimed as a dependent by someone else.
• They are a U.S. citizen, resident alien, national, or a Canadian or Mexican resident.
• They aren’t filing a joint return with their spouse.
• They are under the age of 19 (or 24 for full-time students).
  • No age limit for permanently and totally disabled children.
• They live with you for more than half the year (exceptions apply).
• They didn't provide more than half of their own support for the year.

Qualifying relative

• They don't have to be related to you (despite the name).
• They aren't claimed as a dependent by someone else.
• They are a U.S. citizen, resident alien, national, or a Canadian or Mexican resident.
• They aren’t filing a joint return with their spouse.
• They lived with you the entire year.
• They made less than $4,150 in 2018.
• You provided more than half of their financial support.

When you add someone as a dependent, we'll ask a series of questions to make sure you can claim them. While you no longer receive an exemption for your dependents, there are other tax benefits you may be able to get when you claim a dependent.

If your fiance was 19 at the end of 2018, not a full time student and earned more than $4,150 in 2018, then no one can claim him as a dependent.

If he was a full time (high school) student for over 5 months (he graduated June 2018) and earned more than $4,150 does that constitute him as a dependent even if he wasn't living with her for over half of that time?

No, to be considered as a full time student, he has to be enrolled for at least 5 months at a higher education institution (college or university).