Sorry you've been diagnosed with enlarged prostate so young. Just to avoid any doubt, enlarged prostate is nothing to do with prostate cancer and doesn't mean you're at increased risk of prostate cancer.
Millions of men are on Tamsulosin long term, and most have no side effects at all. If you do get any unacceptable side effects, there are some other alpha blockers you can try instead.
The two main side effects are reduced blood pressure, and retrograde ejaculation (where some or all of your semen is ejaculated backwards into the bladder).