Huw Edwards has had (well documented) mental health issues for years.....so no, I do not think he is "playing the mental health card"...... I imagine he is at rock bottom and his reputation and career has been permanently damaged which must be extremely difficult to cope with. I do wish him well and hope he recovers from this.
However, even if not illegal what he has done needs calling out. It is not OK for married, middle aged men to be having sexual contact with teenagers. This sort of sleaze is wrong and it shouldn't just be swept under the rug. This is the lead news anchor for the publicly funded BBC and presenters such as Huw Edwards need to be held to higher standards than most others. He needs credibility when reporting on other scandals or similar news stories and that has been lost.
The BBC will be able to sack him for misconduct/bringing the organisation into disrepute and I think they absolutely should. It is so disappointing. That doesn't mean that I don't wish him well and a swift recovery.