Pot use is much more prevalent and accepted today than it was when I was younger, but you must remember that it IS illegal. Do you want to be with someone who could get arrested and sent to prison, who may get caught up in criminal violence, or who may be doing harder drugs? Also keep in mind that MANY employers have mandatory drug testing (it's nearly universal in the corporate business world and with all large companies) that may mean he can't get a good job. Before you become any more involved with him, you must ask yourself these questions, ask him about his drug use, and make your own decisions. The fact that you're even asking this says that you find his pot use at least somewhat troubling.
If he lies to you or refuses to answer your questions, you need to drop him and walk away.
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