Some people can free dive while snorkeling and get down with the fish Ė but some of us canít. Personally I find it takes a lot more exertion to snorkel than it does to dive. I have yet to tire of diving at Hol Chan. The experience of having HUGE schools of fish that you can latterly swim into and swim with is awesome.
You have been given some very good advice by some very good people. I like to recommend that people do their class room work at home and bring a referral with them. You can do PADI, SSI, NAUI, and possibly some others. The instructors here have various certifications.
There is no reason that any training should take 3 months. The most I have experienced is six weeks and I have known people who got private lessons and were done in a week.
I suggest you do some research ---- And NOTHING beast SCUBA!