If your bf gets another smaller rat, it's just younger and they should get along fine. It's actually better to introduce a younger male so that dominance can be determined quickly and with no fuss. Your rat you said was three months, still young enough to enjoy the company of a new friend. If here were alone for two years, then I would say no don't do it, but he is still young and would love the company.

Just make sure the new rat is a boy and is properly qurantined, so that you avoid transmitting viral infections. Quarantine should be done in a seperate household where there are no other rodents for at least 2 weeks. If this is not an option the new rat needs to be seperated for 4 weeks as far away from the other as possible, in a closed room and his own cage.


Sarah at Lone Star Rats has a very good article on Quarantine.

http://www.lone-star-rats.com/module...rder=0&thold=0