"None who go to her return again, nor do they reach the paths of life"
It is not often clear to the person who is about to pursue a strange woman or man that this is a life-alerting decision. Solomon is standing at the edge of the cliff screaming for us not to jump off! He wants us to understand that taking action on the impulses of the flesh to pursue an adulterous situation will change you and your destiny in major ways.
Notice that he says none who go to her return again. You are not the same. To become unfaithful is huge. In our day the culture around us wants us to believe that sexual license is not a big deal. The world wants us to see this serious sin as a small thing. It is not just a little mistake. God has not changed His mind. It is a big deal. It is a life-altering decision to become unfaithful to your spouse. I remember two pastors who I knew well who had all the promise and potential in the world who threw it all away to kiss and hold women who were not their wives. They didn't even go as far as actual physical intimacy, but they had to resign their ministries. They would never be the same. A few moments were life changing. Our choices do matter is what Solomon is saying. There are some things that are not do-overs. These were separate men in separate situations, but they both were permanently altered by their indiscretion.
God, in His grace, can supply new measures of hope and comfort; but something is lost that can never be regained. Solomon gives a bleak assessment of a person's ability to recover from adultery. They do not reach the paths of life. This would seem best to take paths of life as the best life or destiny that God had marked out for you. You will not get back to that life. You will not attain to the full potential and full measure of accomplishment that was to be yours because of the detour of adultery that you took.
Men and women do not often ponder the things they give up to have a few seconds of illicit passion and pleasure. God, through Solomon, seems to be declaring that the pathway or destiny that He had for you is no longer attainable when you follow the ways of immorality. You alter your destiny just like the Israelites who blasphemed God and changed the blessings and future that God had planned for them. But God held out hope that He would be able to restore the years that the locust had eaten (in the book of Job) and that the glory of the second temple could exceed the glory of the first temple if they would humble themselves. So God's grace is able to triumph in our sin and weakness but realize that the perfect plan of God for our lives will not be attainable because of adultery. We will be shunted onto a plan B.
Solomon is trying to train young people that they should not give up the best that God has planned for a few moments of sexual pleasure. There is a someone whom God has for you. Save yourself for that person. Live out the life that God has planned for you. Fulfill the good works that God has lined out for you.