Such conduct may have worked in feudalistic Europe, but not here, not now. If they are 18 they are free, which means that they can date or have sex with whomever they want. (In actuality, they probably earned that right at age 16 or 17, depending upon the state they are residing in.) If it were me, I would have probably passed one of them a note saying, "Hey, baby, if you want to get married, then, let's run-off and get married."
Of course, the secular law also says you can make porno and distribute it on the Internet. Despite its lawfulness, if someone at SSPX did that, the priest should still have a problem.
Tele could have done what you said, but it's not the best recipe for a stable Catholic marriage to alienate the entire family of your bride.
There's still too much that's unknown about this situation. We're only hearing one side of the story. From the way Tele tells it, he didn't do anything to deserve getting kicked out, but are we really hearing everything? Then again, to get kicked out of the chapel, they'd better have some real dirt on him, some actual misconduct, not just their suspicions.
I don't know exactly what happened, but let me speak of a hypothetical. If a young-ish man of 30 or so named Gelephorus were to be targeted by a mother who sees him as the perfect suitor for her 48-year old widowed daughter -- and if this same Gelephorus begins pitching woo to a 17-year old nubile instead -- and if this mother was sort of the queen bee of the church and had the priest wrapped around her finger -- a situation like this could easily turn sticky.
It sounds like Tele was, at worst, imprudent. We are in America so minds here are colored by the American mindset, which is that interest in a young girl is automatically perverted.
As far as I know, there is nothing in the Catholic religion that is against marrying a teenage girl, except that you are supposed to respect the fair secular laws. Courting a young girl and waiting until she is of marriageable age doesn't strike me as wrong from a Catholic perspective -- someone correct me if I'm mistaken. But from an American perspective, it's simply not done. You would probably have to get special permission to court a younger girl, the priest and the parents would all have to approve, and that isn't what happened.
The dynamic between a teenage girl and a 30-year old man is extremely awkward. You aren't old enough to radiate harmless paternalistic concern, but you're not young enough that it feels all innocent and cute like when two teenagers are conversing in church, and perhaps thinking of marriage ( yes, younger Catholic girls can be very mature spiritually, but there is still that gap in experience. ) It can come off kind of predatory or wolf-ish.
I would only have brief exchanges with a girl this young. I wouldn't sit in the car or the library with her as I've done with older girls there. If I did sit in the library with a 16-year old, people would get suspicious, and though they'd be wrong to be suspicious, it would be understandable. Sometimes you have to anticipate these things and not fan the flames.